Procedural lines/scrabbles
Randomness is one of the hardest thing to achieve. Messing up the coordinates of simple textures might help.

You can try using a checker texture, separate the texture coordinates of one axis of the mapping, and use a wave texture to create distorted lines. Then mix that with another texture to darken some of the lines.



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Then mix that that with other groups of nodes that go in different axes and with different kind of distortions and use other control (or mask) the mix



(click on the image to enlarge)

NOTE: this kinds of setups can get very complex and cumbersome, so it might be easier to pack things in node groups. Also to understand how things are working start with the checker texture only, then add texture coordinates and a separate XYZ to see the result. Then add nodes one by one to understand what each one is doing and how changing size, distortion, detail etc, are affecting the result. There are infinite ways to combine textures, coordinates and mappings and effects. Trial and error will require some time before you find something that works for you.